This invention relates to a phosphorus-containing polymer having phenolic units and its uses. Such phosphorus-containing polymer is useful as a hardener of an epoxy resin composition, and, after being reacted with an epihalohydrin, as an epoxy resin component as well. The products obtained from the phosphorus-containing polymer of this invention have the flame retardant properties of the UL94V-O standard and high heat resistance, and do not contain toxic substances such as halogen or diantimony trioxide.
Because of easy processing, high safety, excellent mechanical and chemical properties, the composite material, especially the epoxy resin material, has been widely used m the field of coating, electrical insulation, construction building mat adhesives and laminated entities. Particularly, since epoxy resins have strong adhesion to reinforcement material such as glass-fiber fabric, no volatiles and small Tankage of the product while hardening, a laminated plate produced by such resins has the advantage of a broad range of usability, good mechanical strength, good electrical insulation characteristics and excellent resistance to chemicals, etc., and has been massively applied to electrical and electronic products.
However, since the demand for finer circuits and higher density of the printed circuit board is increasing day by day, it has been necessary to develop a laminated plate with better electrical, mechanical, and heat resistant processing properties. Widely used at present, he glass mansion temperature (Tg) after hardening of FR4 laminate plate is generally about 130xc2x0 C. Thus, when the temperature of cutting and drilling is over 200xc2x0 C. during the production process of a printed circuit board and over 270xc2x0 C. during the welding process, the plate breaks or cracks easily. Therefore, various laminated plate materials which emphasize high heat stability and high glass transition temperature are constantly being developed. In addition, another important requirement for the laminated plate to possess is the flame retardant properties. The flame retardant properties of a printed circuit board are absolutely necessary, because safety of life and property are involved as the printed circuit board is frequently used in airplanes, automobiles and public transportation.
In order to ensure the flame retardant properties in the laminated plate, substances that separate the flame and decrease burning should be introduced. For laminated plates of epoxy resin/glass-fiber systems, halogen-containing compounds, especially bromine-containing epoxy resins and hardeners, are used, in combination with flame retardants such as diantimony trioxide, etc., so that the achievement of flame retardant standards (as strict as the UL94V-O level) in the laminated plates can be attained However, when epoxy resins reach the level of the UL94V-O standard, in combination with diantimony trioxide or other flame retardants, the bromine content can be as high as 17 to 21%. Diantimony trioxide has been considered as a carcinogen. While bromine generates not only erosive free radicals and hydrogen bromide, aromatic compounds with high bromine content also produce toxic furan bromides and dioxine bromide compounds during the burning process. Thus, the health of the human body and the environment are seriously affected. These are some of the most serious problems in recycling and handling these laminated plates and why it is most urgent to find a novel flame retardant material which can ameliorate the pollution problems resulting from the laminated plates at present.
Phosphorus compounds have been extensively studied and applied to the new generation of flame retardants designed for environmental protection. For example, red phosphorus- or phosphorus-containing organic compounds (such as triphenyl phosphate, tricresyl phosphate, phosphoric acid, etc.) are used as flame retardants to replace halogen compounds to improve the flame retardant properties of the high molecular material or hardened-type resins. However, when these kinds of compounds are added directly to the resin, massive amounts are needed, and the characteristics of the resin material, such as electrical properties, are adversely affected, resulting in difficulties in practice. Recently, for the sake of environmental protection and safety, phospho-epoxy resins have been used to replace bromo-epoxy resins to obtain flame retardant laminated plates. For example, U.S. Pat. No. 5,376,453 has disclosed laminated plate made from epoxy-containing phosphates in combination with nitrogen-containing cyclic hardeners. However, various phosphate epoxides have been added in order to make up for the insufficient phosphorus content and to reach the hardly achievable UL94V-O standard. In U.S. Pat. No. 5,458,978, where epoxy phosphates in combination with nitrogen-containing epoxy resins and metal complexes are used as hardeners, the glass transition temperature of the products is about 175xc2x0 C., and the flame rest properties only reach the edge of UL94V-O (42 seconds, as opposed to the critical value of 50 seconds). U.S. Pat. No. 5,506,313 has related disclosures as well. However, in these patents, the required flame retardant properties and high heat resistance cannot be reached. The present inventors aim to correct the defects of the conventional techniques and have made extensive studies to complete this invention.